The nature of the perianth in Fuirena (Cyperaceae)

The genus Fuirena Rottb. is currently classified in the tribe Fuireneae Reichenbach ex Fenzl (subfamily Cyperoideae), based on the presence of spikelets with many spirally arranged glumes, each subtending a bisexual flower, and because of unique embryo characters. The trimerous Fuirena flowers have two whorls of perianth parts that show a wide morphological variety and various reduction trends. In flowers of F. ciliaris (L.) Roxb., the outer whorl consists of three bristle-like perianth parts opposite the stamens. The three scale-like inner perianth parts alternate with the stamens. The nature and exact position of the inner perianth parts have long been a subject for discussion. In the context of the 'synanthium' hypothesis, some authors have interpreted the perianth parts as floral bracts. Alternatively, the inner perianth parts have also been interpreted as staminodia because of their appearance and position. In this study we present new evidence in favour of a conventional monocotyledonous pentacyclic flower model in Cyperoideae based on SEM observations on the floral ontogeny of F. ciliaris, F. leptostachya Oliver, F. abnormalis C.B.Clarke and F. pubescens (Poir.) Kunth. Our observations confirm a pentacyclic organisation of the flowers within Fuirena, and they corroborate the interpretation of the inner scales and outer bristles as perianth parts